Galaxies thickness

galaxy.morphology.correct_inclination(inc: Union[int, float, astropy.units.quantity.Quantity, numpy.ndarray], q0: Union[int, float, numpy.ndarray]) → Union[float, numpy.ndarray][source]

Correct the inclination using the given disk thickness assuming the mass distribution is an oblate system. Correction is from Bottinelli et al., 1983 and is given by

\[cos^2 i_0 = (q^2 - q_0^2) / (1 - q_0^2)\]

where \(i_0\) is the intrinsic inclination of the galaxy, \(q = b/a\) is the observed axis ratio on the sky and \(q_0\) is the intrinsic axis ratio of the galaxy.

Parameters

  • inc (int/float/astropy Quantity object with unit of an angle or ndarray of one of these types) – observed inclination of the galaxy in degrees (assumed to be \(\arccos b/a\))

  • q0 (int/float or ndarray[int]/ndarray[float]) – intrinsic axis ratio

Returns

corrected inclination in degree

Return type

float or ndarray[float]

galaxy.morphology.correct_I0(I0: Union[float, numpy.ndarray], q0: Union[float, numpy.ndarray], inc: Optional[Union[float, numpy.ndarray]] = None, inc0: Optional[Union[float, numpy.ndarray]] = None) → Union[float, numpy.ndarray][source]

Correct the observed central surface brightness of a double exponential disk when fitted with a single exponential disk due to the effect of finite thickness.

Note

The intrinsic central surface brightness of a double exponential disk is larger than the central surface brightness given by the best-fit single exponential profile.

The reason is that when fitting with a single exponential profile, the inclination is biased because the intrinsic axis ratio is not deduced from it, which means the value is underestimated with respect to the intrinsic value.

The correction is given by (Mercier et al., 2021)

\[\Sigma(0) / \Sigma_{\rm{RT}} (0) = (q_0 \sin i_0 + \cos i_0) / \sqrt{q_0^2 \sin^2 i_0 + \cos^2 i_0}\]

Warning

Provide inclinations in degree.

Parameters

  • I0 (float or ndarray[float]) – observed central surface brightness from the single exponential profile

  • q0 (float or ndarray[float]) – intrinsic axis ratio of the galaxy

  • inc (float or ndarray[float] or astropy Quantity with angle unit) – (Optional) observed inclination in degree (not corrected of the galaxy thickness). If inc0 is given, inc0 is used instead.

  • inc0 (float or ndarray[float] or astropy Quantity with angle unit) – (Optional) intrinsic inclination in degree (corrected of the galaxy thickness)

Returns

corrected central surface brightness

Return type

float or ndarray[float]

Raises

ValueError – if both inc and inc0 are None

galaxy.morphology.disk_thickness(z: Union[float, numpy.ndarray]) → Union[float, numpy.ndarray][source]

Code author: Wilfried Mercier - IRAP <wilfried.mercier@irap.omp.eu>

Return the thickness of MS disk-like galaxies (see Mercier et al., 2021) prescription as a function of redshift.

Parameters

z (float or ndarray[float]) – redshift

Returns

disk thickness

Return type

float or ndarray[float]

Raises

TypeError – if z is not an int, float, np.float16, np.float32, np.float64 or a ndarray